Field of the Invention
The invention relates to a multi-layer circuit board and a manufacturing method thereof. More particularly, the invention relates to a multi-layer circuit board having a cavity and a manufacturing method thereof.
Description of Related Art
In order to increase the application of printed circuit boards (PCB), a variety of technologies have been developed in recent years to manufacture printed circuit boards having multi-layer circuit structures for increasing the internal space for circuit layout. A manufacturing method of a multi-layer circuit board is to repeatedly stack and laminate a build-up structure, composed of a copper foil and a prepreg (pp), onto a core board to increase the internal layout space of the circuit board and utilize an electroplating process to fill a conductive material in a through hole or a blind hole of each build-up structure for conduction between the layers. In addition, various types of elements, such as chips, connectors, optoelectronic components, or heat dissipation elements, may be disposed in the multi-layer circuit board as required to add functions to the multi-layer circuit board.
To avoid increasing the thickness of the multi-layer circuit board when electronic elements are added, some manufacturing methods may include forming a cavity in the multi-layer circuit board for disposing the electronic elements, so as to embed the electronic elements in the multi-layer circuit board. The conventional methods form the cavity in the multi-layer circuit board by performing laser drilling or CNC drilling after the multi-layer circuit board are formed through repeatedly laminating the build-up structures on the core board. In order to precisely form the cavity having the desired size on the multi-layer circuit board, high-precision instruments are required for depth control during the manufacturing process. In addition, it is difficult to form a straight shape at the junction of the bottom and the sidewall of the cavity, so that undercut may occur and the bottom of the cavity may become uneven easily after being processed. Further, the processing costs increase with the depth of the cavity.